For fall overseeding you may want to match the type of grass you already have, so the lawn’s color and appearance will be uniform. In the North, however, your other choices look almost the same as Kentucky Bluegrass and there are some benefits to sowing more than one type of grass in your lawn. Every grass has particular fungal diseases to which it is susceptible. Combined, (Kentucky bluegrass and perennial ryegrass for example) they reduce the chances of losing major portions of the lawn to any one fungal disease problem. One grass may get a disease, but the other type will be immune and keep the lawn looking good. See the section in Helper Choosing Lawn Grass Seed.
Calculating How Much Seed
Estimate the size of your lawn in terms of 1000's of square feet and follow instructions on the package label. Recommended sowing of Kentucky bluegrass, for example, is 2 or 3 pounds for every 1000 square feet. At that rate it takes 20 to 25 pounds of seed for an 8000 square foot lawn.
Amount of Grass Seed Per 1000 Square Feet of Lawn
Kentucky bluegrass - 3 lb.
Perennial ryegrass - 8 lb.
Tall fescue - 8 lb.
Fine fescue - 4 lb.
Common Bermuda (hulled) - 2 lb.
Centipede - 3 lb.
Bentgrass - 1/2 lb.
Sow Grass Seed
Rake Seed for Soil Contact
It is important to insure that the seed is in contact with the soil. So the next step is to lightly rake over the lawn surface to bring the seed into contact with the top 1/8 inch of soil that has been loosened by the dethatching process.
Spread Topdressing (Optional)
Topdressing means to spread a thin layer (no more than ¼ inch) of topsoil, compost or peat moss over the turf that you have overseeded. An even covering about ¼ inch thick does not require much of the material, but there is enough to protect the new seed and help keep it moist.
Some yardeners like to lightly tamp the topdressing over the new seeds by going over the area once with a lawn roller filled about 1/3 with water. For small lawns, simply walking on the topdressing does the trick. This slightly tamped soil will hold moisture near the seed longer. If you choose not to topdress your overseeded lawn, simply water more often to assure that the new seed does not dry out.